In this image, I’ve covered energy as it passes from the sun in the form of light to the chloroplast of plants. In the chloroplasts, there are structures called thylakoids where the magic happens. This is where photosynthesis takes place in two parts, 1) light-dependent reactions and, 2) Calvin Cycle.

The waste products here are eliminated and the useful products are then sent to the mitochondria. The first step is 1) glycolysis, followed then by 2) the Krebs cycle (also called the Citric Acid Cycle) under aerobic conditions OR, 2) fermentation (under anaerobic conditions)

There’s a LOT of stuff that happens here. These are the basics. This stuff can get extraordinarily complicated–the guy the Krebs cycle is named for won a Nobel prize for his work!

I’ve never, personally seen an image that attempted to go from the sun to photosynthesis to cellular respiration but I tried to keep it as simple as possible. That said, if you feel something’s missing, its probably because it is. Some steps weren’t explicitly mentioned for simplicity’s sake.

One final note: ATP gives you a burst of energy. If you need energy to do anything for longer than about a minute and a half, you want sugar. Sugars provide longer-lasting energy. ATP (which makes up about a half-pound of your total body weight) doesn’t store, in other words, it gets used shortly after it’s made. ATP actually gets recycled over 1,000 times a day by humans!

In your youth was Sesame Street. If you were lucky when you got older there was Bill Nye. Now it would seem you’re too old for education set to music. But if that’s what you think, you’re wrong. Check out these tunes:

Thanks to ProfDodd for the tip – They Might Be Giants sings all things science on their album (that’s a CD for you young’ns) rightfully titled Here Comes Science. Listen to track previews on Amazon.

Rapping is taken to a new level by a couple of guys from Stanford. This video is timely for what we’ve been talking about–ATP, energy, glycolysis–but check out his YouTube page for lots of great videos.

Heterotrophs need to obtain energy from consuming autotrophs. Remember autotrophs turn light energy into chemical energy, which is stored as the sugar glucose. The process of releasing energy by breaking down glucose and other food in the presence of oxygen is called cellular respiration.

Cellular respiration is not exactly, but can be roughly viewed as, the reverse process as photosynthesis. Oxygen and glucose combine to breakdown and reassemble as carbon dioxide, water, and energy.

6O2 + C6H12O6 -> 6CO2 + 6H2O + ATP

oxygen + glucose -> carbon dioxide + water + energy

This process is simplified of course. There’s a whole confusing mess of glycolysis, ATP, and NADH which the average high school bio teacher would want you to know, but honestly it’s overkill (…it’s not even in our state standards…).

Now there are cases when cells don’t get enough oxygen. In this case, the cells produce nasty waste products that they remove from their body. Some microorganisms, such as yeast, produce alcohol in the absence of oxygen. This is called alcoholic fermentation. Other organisms, such as yourself, produce lactic acid in the absence of oxygen. Fittingly, this is called lactic acid fermentation. Fermentation is vital in our food system. Production of alcohol is quite the large business throughout the world; as is production of foods such as yogurt and pickles which utilize lactic acid.

One last point of overkill: the Krebs cycle and electron transport chain. Unless you go to college for Biology, you have no need for this… and honestly, I went to college for Biology and I don’t have a use for it, short of torturing students with it if I was an evil person.

Previously you read about autotrophs and heterotrophs. The difference being in the way they obtain energy. Plants are autotrophs, and today I’d like to focus on how plants get the energy they need.

Plants need the following things to get energy to live:

Water (H2O)

Carbon Dioxide (CO2)

Sunlight

The process of converting H2O and CO2 in the presence of sunlight into energy is called photosynthesis.

In order for the water to get to the leaves of a plant where photosynthesis takes place, it is absorbed from the surrounding ground through roots and is brought up through tissue like your blood vessels.

The carbon dioxide is absorbed my the leaf directly through openings (or pores) on the under side of the leaf.

Light-absorbing molecules called pigments capture sunlight for the plant. The primary pigment in plants is called chlorophyll. Chlorophyll gives plants their green color because it absorbs reds and blues and reflects green!

Chlorophyll is housed in organelles called chloroplasts. This is where photosynthesis takes place.

Every organism needs energy to live. But where does that energy come from? Let’s find out…

There are two types of organisms: autotrophs, which make their own food, and heterotrophs, which must consume food from an outside source.

Most autotrophs convert light energy from the sun into usable energy. These are the only types of autotrophs you need to be concerned with for now. Your typical autotroph would be any plant, a grass, a tree, a shrub. Unicellular organisms can be autotrophs too!

Examples of heterotrophs include animals, such as yourself or a lion, as well as fungi plus some unicellular organisms like some protists or bacteria.

Energy comes in many forms. We already mentioned light energy from the sun. There’s also heat energy and other types like the electricity that powers your television.

The type of energy that cells can best use is chemical energy. Specifically it’s in the form of a chemical called ATP. Really the only thing you need to know is that ATP is like a fully charged battery. A bond is broken and energy is released. That turns ATP into ADP. Or you can think of it like this A3P =>release of energy => A2P. ADP is like a battery waiting to be recharged.

ADP + Engery stored = ATP

For some reason this seems to really trip people up. If you have any questions, drop me a comment or a tweet @AmoebaMike.

After discussing the cell, it would only be fitting to talk about how the cell gets nutrients in and waste out. The cell is surrounded by the cell membrane, which acts as the gate for everything that needs to pass into and out of the cell.

Particles will move freely across the cell membrane until equilibrium is reached. Equilibrium means that the concentration (amount) of a substance is the same on both sides. When the concentration of a substance is greater on the outside of the cell membrane, the particles will move across the membrane from the higher side to the lower side until both sides are equal. That process, where particles move from an area of higher concentration to an area of lower concentration, is called diffusion. In the case of water, diffusion gets a special name: osmosis. Osmosis is the diffusion of water.

Diffusion and osmosis occur naturally with the random movement of particles, so they cost the cell no energy.

Some particles are too big to properly move through the cell membrane, so the particles are helped across the membrane. Facilitated diffusion is when particles move across a cell membrane through a protein channel. Because the particles are still moving with the concentration, not against it, facilitated concentration costs the cell no energy. However, sometimes the opposite of facilitated diffusion occurs. Active transport is the process where a cell uses energy to move particles from a lower concentration to a higher concentration. Again proteins are used to make this process work, but instead of protein channels, they’re called protein pumps.

Below you’ll find an animated gif that shows the process of diffusion of 2 blue particles, which we’ll call water, and the facilitated diffusion of 1 green particle, which we’ll call glucose. The animation was originally done in Flash, but I couldn’t host a SWF or even a movie file for free, so I had to convert it to a GIF. Maybe if these videos catch on I’ll do the YouTube thing, but for now I hope this works.

To go just a little further in depth as to what we meant last time when we discussed the characteristics of living things, I wanted to make a follow up post. I’ve been putting this off, but it’s time to bite the bullet.

All living things are made up of 1 or more cells. Cells are the basic unit of life. Most are smaller than you can see with the naked eye, but they are composed of different parts called “organelles” that work together to allow the cell to function and reproduce.

All living things reproduce. Reproduction creates offspring, which are similar, but not identical to the parent(s). Reproduction can be sexual (two parents) or asexual (one parent).

All living things are based on a genetic code. Usually that code is DNA (but sometimes RNA in the case of some viruses, which remember are technically not living), which is a molecule that tells your cells what to do in order to function. Essentially the genetic code is a set of instructions for your cells.

All living things grow and develop. Some organisms simply grow larger and prepare for reproduction. Other organisms may develop legs or wings for movement, or teeth for chewing, or breasts for feeding their young.

All living things obtain and use energy. Just as you need food, so do plants, fungi, and even bacteria. The sum of all chemical reactions to build up and break down materials is called metabolism.

All living things respond to their environment. A stimulus is a signal to which an organism responds. When you get pollen in your nose, you sneeze. When soil is moist and warm, a seed germinates. When you turn on a light, roaches run away!

All living things maintain a stable internal environment. No matter what goes on outside the body, all organisms keep their internal conditions stable. The process to do this is called homeostasis. When you get cold, your body tries to keep your internal temperature from dropping too much. So you begin to move involuntarily. We call this shivering. Likewise, if you’re too hot, you’re body sweats to cool you off.